The invention relates to a high-pressure vessel with inner closure which is especially suitable for frequent opening and closing for the purpose of filling and emptying the vessel.
Modern process technology is unimaginable without high-pressure vessels. For instance, synthesis or polymerization processes require high-volume pressure vessels having been designed for pressures of 500 bar and more. However, such pressure vessels as used for ammonia synthesis or ethylene polymerization are normally in operation for longer periods, i.e., several months or years, and at the same pressure load. Major pressure variations are mainly to be expected during start-up and shutdown of such high-pressure plants.
As the cylindrical shell of a pressure vessel represents the greatest material portion, numerous designs aimed at optimizing the quantity of material required have been developed.
A summary of such designs is given by H. Strohmeier in Rheinstahl Technik, 9th year of publication, Volume 3/71, page 104 and following, and by J. Ehle and A. Pollanz in Chemikerzeitung, 95th year of publication (1971), No. 1, page 28 and following.
The closure of high-pressure vessels is of special importance. Depending upon the application, a high-pressure vessel is equipped with two removable closures or with one removable and one welded-on or forged-on bottom. While the so-called outer closures, the cover of which rests on the pressure vessel flange and is fixed by stud bolts or clamps, can only be used for high-pressure vessels of small diameters, the closure becoming otherwise too heavy and inoperable and thus too expensive with regard to fabrication and mounting, the inner closures have a wide range of application.
VDI-Z. 104 (1962) No. 11, page 479, refers to an inner closure for a high-pressure vessel which consists of a cover, a tapered sealing ring, several segments of a supporting ring, bolts for fastening the segments, and a retaining ring. The vessel closure is designed so that the vessel is pressed against the tapered sealing ring which, on the one hand, is supported by the vessel shell and which, on the other hand, diverts the axially-acting force components via the horizontal supporting ring faces into the vessel flange. The integration of the tapered sealing ring into the force flux of the cover supporting system causes high taper area loads involving the risk of damage or welding. In order to obtain the full effect on the sealing face, the surface finish must be extremely high. Before subjecting the vessel to the inner pressure load, a prestress is applied to the tapered sealing ring by means of the cover tensioning bolts and the retaining ring so that the closure is already tight when the inner pressure is built up. However, this type of inner closure is inappropriate for frequent closing and opening because the manual operation of the covers is extremely time consuming.